Temperature compensated force and motion transmitting hydraulic system



Aug. 29,1950 1 s.

' TEMPERATURE COMPENSATED FORCE AND MOTION I. M DUFF TRANSMITTINGHYDRAULICSYSTEM Filed 00 15, 1944 v INVE/WU)? 57/14/10 1 Mew/7 ATTORNEYair ' s. M DUFF 2,520,731 TEMPERATURE COMPENSATED FORCE AND MOTION ITRANSMITTING HYDRAULIC SYSTEM 7 .3 Sheets-Sheet 2 Filed 001'... 13, 1944Filed Oct. 13, 1944 Y S. l. Ma DU .v TEMPERATURE COMPENSATED F E ANDMOTION TRANSMITTING HYDRAULIC SYSTEM v :3 Sheets-Sheet 3 ATTORNEYPatented Aug. 2?.9, 1950 TEMPERATURE oo PENsATEn FORCE AND MOTIONTRANSMITTING HYDRAULIC SYSTEM 7 Stanley I. MacDufi, South Bend, Ind.,assignor to Bendix Aviation '00 rporatiqn, South Bend, V

Ind., a corporation of Delaware 7 Application October '13, 1944, SerialNo. 558,586

9 Claims. 1

This invention relates .to control means for hydraulic systems of theclosed .circuit type and more particularly to a mechanism which willinsure identical operation of both transmitter and receiver of such asystem. t 7

Closed systems of this type are commonly used in aircraft where it isdesirable to remotely con trol wing flaps, rudders, ailerons, etc., froma central point within the aircraft. It is obviously importantto thepilot of the aircraft that he know, by moving the transmitter lever apredetermined distance that the receiver lever, to which the wing flapsor other apparatus is attached will move a like distance, 'It is equallyimportant to the pilot that, once a setting. of the apparatus is madefor a predetermined flight, the setting will not be disturbed'due toextraneous factors such as temperature changes which cause-a variationin the volume in the hydraulic fluid. Although the device of theinvention is discussed in connection with its use on an aircraft it isunderstood that it is not limited thereto;

It is, therefore, an importantobject of this in! ,vention; to provide amechanism which will com-. pensate for volume variation of a liquid in ahy-. draulic system causedby temperature changes It is another veryimportant object of the-invention to provide a mechanism for a two-pipeline liquid pressure system of the closed circuit type which willautomatically. compensate for volume variation due to temperaturevariation .of the liquid.

v A further object of the invention resides in the provision of acontrol means having'twoareas each of which is exposedto liquid pressureof a hydraulic systemto compensate for volume variation due totemperature variation of a fluid.

7 A still further object of the invention resides in the provision ofcontrol means including a, pair of oppositely disposed pistons subjectedto a predetermined comm-on force on one side and system pressures on theother side to compensate for volume variation due to temperature changeof a fluid. 1

Another object of the invention is to provide a means for determiningthe loss of fluid in a system of the type herein disclosed.-. V Furtherobjects and advantages of the present invention will be'apparent fromthe following description, reference being had to the accompanyingdrawings wherein a, perfected form 'of the invention is clearly shown.

In the drawings:

Figure 1, diagrammatically illustrates the in- (Cl. GO-54.5)

'mitteror receiver.

1 i system of the closed. circuit type. The control mechanism per se ofthe invention being shown partly in longitudinal sectional view; PFigure 2 is a view partly .in section taken 'sub-. stantially on line2--2 of the control mechanis shown in Figure 1;

Figure 3 is a view taken on the line 3--3 of F'ig-' ure -2 with portionsof the mechanism remove forpurposes of clarity Figure 4 is a plan viewof the dial and graduated cap as viewed from line 4-4 of Figure 2;Figure 5 showsa view in longitudinal section of amodified form of theinvention; and.-

Figure 6 is a=transverseview partly in section taken on the line 6--6 ofFigure 1- Referring now to Figure 1 which illustrates a closed'hydraulicsystem, the reference numerals l0 and I2 designate fluid motor unitswhich for purposes of exemplification only will be termed thetransmitter and receiver units respectively.

In the. system shown the receiver unit incorporates the controlmechanism but as hereinbefore pointed out the receiver unit might aswell be the transmitter unit insofar as the function 'of the two unitsin the system isooncerned. That is, it makes no difierence'whether themotor unit to which the temperature compensating control mechanismisfincorpo'rated is utilized as a trans- The fluid motor unit 10 includes a body or cylinderv l4 bored at It for the reception of a piston"l8 having a shaft!!! connecting a lever or handle 22 fulcrumed at 24 tothe bracket 26 which is an integral part of the body. A link '28connects the shaft 20 to the lever 22 to thereby provide an articulateconnection between the shaft and lever. A bearing member 30 recessed at32'and groovedat 34 for the reception of seals 36 and 38 respectively isdisposed in each end of the bore I6 to provide bearing-surfaces for theshaft 20. The piston l8 has anannular groove 40 adapted to receive 'aseal 42. to thereby provide two chambers and 46-.within the cylinder H.The cylinder is drilled unit to the system. I The cylinder l4has-integral therewith an enlatgedbo'dy portion 52 drilled at 54 and 56coun- 'terbored at 58 and 60. These drilledportions intersect to form apassage connecting. opening." to opening 50 for by-passing fluid fromchamber 44 to chamber and. vice versa. The junction of the drilledportions-.54 and 56-with the coun- --terbores,.58 andv 60 respectivelyform valve seats Gland. which cooperate with valves'66 and,

with a rack 2I2'adapted to cooperate with the pinion II8 for rotatingthe same. The pistons I94 and I96 are equipped with seals 2I4 to form a'chamber'2 I6 which is sealed from system pressure. Chamber 2I6 is incommunication with chamber I88 through a restricted passage 2I8.'Chambers I88 and 2I6 contain fluidwhich is put under pressure by theadmission of gas to chamber I90 through an opening 220. The pressureofthe gas acting on the flexible member I92 is transmitted to the fluidof chambers I88 and 2 I65 The restricted port 2! tends to minimize theeffect of shock waves created by an attempt to suddenly move" pistonsI94 and I96. That is, any attempt to suddenly move the pistons againstthe incompressible fluid will be retarded by fluid friction in therestriction 2I8. I

"To prepare the system for use the chamber I4 is put under agas'pr'essure which is'determined by the maximum load to be applied tothe transmitter and in all cases the pressure in this cham'- ber must beat least half of the applied transmitter'p'ressure. Obviously, if thepressure in chambr-I4 were anything less than one-half the appliedmaximum transmitter pressure the pistons 94 and 96 would collapse or beforced toward each other when maximum load was applied to thetransmitter. v When-the chamber I4 is put under the desired pressurewhich is determined by the maximum load to be applied to the transmitterand'the system filled with a fluid such as oil until the pistons aresubstantially in the position shown to allow for expansion andcontraction ot the fluid due'to temperature change, the levers 22 andI26 are-{then adiusted to occupy the 'same relative positions. Thisadjustment is accomplished by raising the centralizing valve 68 fromseat 64 to establishcommunication between chambers 44 and 46"through thepassages 54'and 56 which connect the two sides of the system. Opening ofthe valve 68 to allowiree communication between the chambers 44 and 46permits movement of piston I8 of the motor unit without transmit tingalike movement to the pistons '94 and 96 since the oil in thetwo'chambers of the motor unit I0 is free to pass from one end of themotor unit to the other end. After the adjustment has been completed thevalve 68 is closed. It is to be noted that the pressure in the systemunder static conditions, that is, with no force applied to' thetransmitter, is the same as the pressure in chamber I4 since thepressure in this chamber is acting equally on the pistons 94 and 96 uring them against the fluid of the system. Bleed valves 66 and I6 arelocated in strategic positions in the system for purging the system ofair. j, The operation of the automatic control mechanism which isresponsive to change in volume due to temperature variation is asfollows:

, With the pistons of the motor unit I0 and I2 in the positions shown inFigure 1, assume a rise in temperature of the fluid in the system. Thistemperature rise caused by a change in ambient will bethe same in bothof the lines 84 and 86 since these lines as aforementioned parallel eachother. This temperature rise also will increase the volume of fluid inthe system. The increase in volume of fluid is compensated for by thecollapse'of pistons 94 and 96 which move toward each other against thepressure in chamber I4. The movement of the pistons caused by equal opposed pressures acting in chambers I06 and I08 dueto volumetricvexpansion rotates the pinions II8 which engage racks II 4 and H6without dis- 96 to the right with a consequent movement of lever I26 anamount equal to the angular displacement of lever 22. Under theseconditions of differential pressure it is to be noted that the pressurein chamber I4 acts on the opposite sides of the pistons-to the systempressure in a manner to prevent rotation of the pinions II8 on pin I201-Stated another way, the increased liquid pressurein chamber I06 will begreater than the pressure of the'ela'stic medium in chamber 14 to createa resultant force to the right and the reduced pressure in chamber I08is less than the pressure of the elastic medium I4 to create a resultant force to the right, At this time the pis tons 94 and 96 functionas a single piston rigidly and immovably fixed to shaft 92. The forcesacting on pinions II8 are balanced, that is,the' moment of force tendingto'rotate the pinions clockwise, which moment of force is the differential pressure in chambers I4 and I06 acting on piston '94, is equal tothe moment of force tending to rotate the pinions counterclockwise whichmoment of force is the differential pressure in chambers I4 and I08acting on piston 96. These balanced forces acting on the pinion areresolved into a single component of force which is transmitted throughthe racks and pinions to the shaft 92 which is accordingly moved. Thatis, the differential pressure in chambers I06 and I08 move the pistonswhich at this time are relato the shaft. In the modified form, Figure'5, the piston shaft has been eliminated and in its stead the sleeve 2I0has been substituted which is connected to the lever I60 which is driventhrough the pinion I18, rack 2I2, sleeve 2I0, pin 208, pin ion 206 andracks 202 and 204. Should there be a change in fluid volume in thesystem due'to temperature variations the pistons will move toward 'oraway from each other to thereby rotate compensating pinion 206 withoutaffecting movement of the lever I80.

I claim:

'1. In a closed hydraulic system havinga force transmitter unit and areceiver unit, one of said units having a central chamber, fluid underpressure in the central chamber, a pair of pistons relatively movableand arranged end to end in said chamber so that the adjacent ends onlyof said pistons are subjected to the fluid pressure in said chamber tothereby tend to move the pistons in opposite directions, end chamberscon taining fluid under pressure located at the remote end'of saidpistons to oppose the aforesaid movement of said pistons, connectionsbetween said end chambers and said other unit, a rack on the adjacentend of each of the pistons, and a pinion disposed in a manner to engagethe racks and constructed and arranged so that when the pistons aresubjected to a pressure differential acting on said remote ends thereofthe pretons are heldrelatively immovable with respect to each otheralthough movable as a single piston within said one unit, and when saidremote ends of the pistons are subjected to pressure changes due tovariations in temperature of the 'tively immovable with respect to eachother and fluid :in said end chambers the pistons are relatively to eachother. V

Ziln .QL'iClB-Sfid hydraulic system having a 21331706 transmitter-muttand ;a receiver unit interconnected, means associated with force transniiitterfunit .foreppIyi-ng a :force thereto which mill be transmittedto the receiver unit, ,a mem ber asscciated with the receiver to bemoved to response to the tome applied to the tramsmitter one of saidunits comprising ;a cyl indmiga pair of :pistons coaxial'ly arranged thecylinder and relatively movable, a chamber associated with the cylinder,fluid under pressure in the ch-amber, said flu-id acting 'on one face ofmoved 7 each of *lflie pistons tending to separate flnidiinithe otherunit and in the ends of the cylhinder ,for acting onthe :other .fiace of.each of the tending to oppose separation thereoi a rackron each of thepistons, and means for drivaiiiyri-ntnrcnnnecting said pistons,saidwlast-named means including a pinion in driving engagement withracks and constructed :and arranged so when :a force applied to said(other unit is transmitted to ,one or the other ofsaid other face of thepistons the pistons will move together as nne 'pis-ton to cause movement.of the member, and the zpnessure change :in said system due toterrmerazture variation (of the fluid is -transmitted to said other race.of each :of the pistons rfimultaneously the pistons will moverelatively to cachother, whereby the position of :the memremains=-unaffected. r Ifi'gClDSSd hydraulic system having a dome transmitterunit and a receiver innit interconnected, means associated with the sometransmitter unit ,for'vapplting :a tame thereto which will betransmitted to the receiver unit, :a menther associated with thereceiver unit "to hemoved response to the force applied to thetransmitter unit, a pair of pistons coaxialfly disposed end to end inone of the units and constructed and arranged ."for relative movement, apressure chamberrformed in said one unit at the adjacent ends of thepistons :to subject said ends to pressnne tending to urge them apart,fluid under jected to pressure changes-due to variations in temperatureof the fluid acting on said remote .mdsthe pistons are movedrelatively-to each other :to prevent movement of said member.

4. lnsa closed hydraulic system having a tonne transmitter and areceiver unit-interconnested, means associated with the forcetransmitter unit for applying .a force thereto which will hetransmittedto the receiver unit, ,amember associated with the receiver unit to :bemoved in responseto the iorce applied to the-transmittor a pair-ofpistons coaxially disposed end to end in one of the 'units and havingrelative movement, .-a pressure chamber for-med in said one unit at theadjacent ends of the pistons to subject said ends topr-ess-ure tendingto urge them apart, fluid under -pressure in the other unit-andaeting'ion the remote ends of said pistons tend ing to pnevient them,trom being urged apart, as sleeve sli'dably disposed in said one unitand formed with, a rack exteriorly thereof, a pinion rotatably carriedJoy said sleeve and positioned interiorly -.thereof,, arack integralwith said adjsacent of the pistons and constructedand arranged to .meshwithsaid pinion, and a .second ,pi-nion in mesh with the rack on saidsleeve and :drivably connected to ,said member, the at, rangement ofsaid first mentioned pinion :and said pistons being .=such that when:the pistons are subiected to a difierential pressure acting on theremote ends thereof the pistons are held immovable with respect to-.each other although movable a vsinglepiston to slide said sleeve :tocause said member 1301136 moved, and when remote ends or the pistonsaresubjected topmosure changes :due to variations in temperature -of thefluid acting $9 11 said remote ends pistons are moved relatively-to each:other to prevent movement :ofqsaid member.

combination with a temperature nompensating mechanism for use in aclosed icydraulic system in which it is desirable to maintain apredetermined volume of liquid the system, ,a motorunit having a pair ofrelatively movable pistons therein, means including a pinion drivablyinterposed between't-he pistons so as-to cause them to .move toward eachothermt times and away from seach' other at other a pressure chamber,pressure the ohamberacting on said pistons inaa manner tending to movethem away from each other and at the same time put the hon-id oi thesystem under presurea transparent cover for said chamber, :a graduatedmemherzmounted :adiaoentthe -.charnber, and an indicator in the'cham-berviewable-through the transparent cover and rotatably connected itspinion, :said indicator being set :to :point tore pnedeterininedgnaduationunder known eonditimas oi liquid temperature and volume,whereby :3 change in the volumenf liquid in the a designated temperaturewill causethe pinion to rotate the indicator to aposition on thegraduaited member indicating the change.

. 6. In a closedhydraulic system having eyioroe transmitter unit and areceiver unit interconnected, means associated with thesforcetransmitter unit {or applying ,a .ionce themeto which mill-betransmitted to the receiver unit, a her associated with the receiverunit to .be moved iii-response the .force applied to the transmit terunit, ,a pair of pistons coaxially disposed end to end inthereeciverunitand constituted ior relative movement, ,a pressure chamber formed insaid receiver at the adjacent ends of the pistonsto subject said ends topressure tending tourge them apart, fluid under pressurein saidtransmitter unit and acting on the remote tends of said pistons tendingtopreventthem iromsbeing urged apart, a sleeve .slidably disposed innaidreceiver unit and formed with a rack exteriorly thereot, a pinion r-rotatably carried by said ,sleene and ,positioned interiorly thereoi, aintegral with said adjacent ends of the pistons and constructed andarranged. .toqmesh with 'said pinion, ,a second pinion Lin :mesh withthe rack ion said sleeve and :drivablyponnected to said mom-.- icer,,thewarrangement cisaid first mentioned and said pistons being such thatwhen the :pistons are subjected to a difierential pres sure acting onthe remote ends thereof the pistons are held immovable with respect toother although movable as a single piston said sleeve to cause saidmember to be moved, and when the remote ends of the pistons aresubjected to pressure changes due to variations in temperature of thefluid acting on said remote ends the pistons are moved relatively toeach other to prevent movement of said member, and means associated withsaid pressure chamber for controlling the rate of relative movementbetween the pistons when the movement is caused by sudden loadstransmitted to said pistons from said transmitter unit. I

'7. In a closed hydraulic system having a transmitting device and areceiving device, ;a pair of conduits, one conduit connecting one end ofthe transmitting device to one end of the receiving device and the otherconduit connecting the other end of the transmitter device to the otherend of the receiver device, a pair of pistons in one of said devices,said pistons being coaxially arranged end to end, said one deviceincluding a chamber therein formed at the adjacent ends of said pistons,fluid under pressure in said chamber and acting on the adjacent ends ofthe pistons tending to urge them apart, fluid in said conduits and inthe ends of the devices and acting on the remote ends of said pistonstending to prevent them being urged apart by the fluid under pressure insaid chamber, a rack on the adjacent ends of the pistons, a shaft onwhich the pistons are slidably arranged, a member connected to the shaftfor movement, and a pinion engaging the racks and rotatably iixed to theshaft, said pinion being arranged so that when the pistons are subjectedto a pressure diflerential acting on the remote ends thereof the pistonsare held immovable with respect to each other although movable as asingle piston within said one device to permit movement of said member,and when the remote ends of the pistons are subjected to pressurechanges due ,to variations in temperature of the fluid in said conduitsthe pistons are moved relatively to each other to 10 compensate forchange in volume of the fluid in the conduits.

8. A force transmitter or receiver unit comprising a cylinder, pistonsco-axially arranged in the cylinder, means located externally of thecylinder for applying force and motion to the pistons, and a mechanismconnecting the pistons to said means in a manner such that the pistonsmay move together with said means as a unit or equal distances inopposite directions relative to said means.

9. A force transmitter or receiver unit comprising a cylinder, pistonsco-axially arranged in the cylinder, means for applying force and motionto the pistons from the exterior of the cylinder, and a mechanismconnecting the pistons to said means, said mechanism including a memberpivotally carried by said means and connected to adjacent ends of saidpistons so that the pistons may move together with said means as a unitor in equally opposite directions relative to said means.

STANLEY I. MACDUFF.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

